Photographic printing material



Patented June 19, 1945 Maximilian Paul Schmidt, Wiesbaden-Biebrich, andGottlieb von Poser, Wlesbaden, Germany; vested in the Alien PropertyCustodian No Drawing. Application March 29, 1943. Serial No. 481,063. InGermany August 5, 1940 13 Claims.

The present invention relates to a process of enhancing thelight-sensitiveness of photographic printing material containing diazocompounds.

It is already known that photographic printing materials can be obtainedby means of light-sensitive diazo compounds. Diazo compounds which aresuitable for such a process have to satisfy, as is known, a great numberof requirements. Many diazo compounds are known which in variousrespects are well suitable for diazotype purposes, but nevertheless havenot acquired any practical. importance, since theirlight-sensitivenessis too small.

The various colorless or only slightly colored diazo compoundsparticularly belong to said kind of diazo compounds. The afore-nameddiazo compounds are in most cases distinguished by the fact that thephotographic prints prepared therewith have only a slight tendency toturn yellow. Moreover, they are particularly suitable for the productionof reflex copies. They yield reflex copies very rich in contrast.Furthermore the dyestuffs forming the picture of the reflex copiesstrongly absorb chemically active light if suitable azo-components are.used as this is described in detail in the co-pending U. S. patentapplication Serial No. 27 6,420 filed May 29, 1939, now Patent No.2,246,425. The reflex copies are therefore well suited for beingreproduced on photographic printing paper, for instance diazotype paper.In spite of these favorable properties the diazo com pounds in questionhave acquired only very little practical importance since theirlight-sensitiveness is much smaller than that of the usual c01- oredamino-diazo-compounds and diazo-anhydrides. In comparison with'thelatter they require an exposure to light which, for instance, is

three to ten times as long or even longer.

The termsrelatively light insensitive diazo compound" or diazo compoundof small lightsensitiveness respectively in the following descriptionand the claims mean diazo compounds the light sensitiveness of which isabout at most a half of that of the 1-dlazo-4-dimethyl-aniline providedthat a usual source of light, for instance the arc lamp is employed forthe exposure.

In the co-pending U. S. application Serial No; 373,139 filed January 4,1941, now Patent No. 2,322,982, there is described a process ofenhancing the light-sensitiveness of photographic printing materialcontaining relatively light-insensitive diazo compounds. In said processaromatic ketccompounds are used as sensitizers.

On further investigating the process disclosed in the afore-namedapplication we have now found that quite generally such organicsubstances free from heavy metals are useful sensitizers, besides theketo-compounds named, as show a strong absorption of light within thesphere of the spectrum adjacent to the sphere of absorption of the diazocompounds towards the long waves.

. In general it is advantageous if the sensitizers absorb light'within asphere of about 3300 to 4400 Angstrom, It is, however, not necessarythat the sensitizers show a considerable absorption over the whole ofsaid spectral region, though this is advantageous. It is suflicient ifthey absorb light in part of the region named. It is, however, desirableif the substances absorb light particularly in those parts of thespectral region named in which the usual sources of light, for instancethe mercury vapor lamp or the arc lamp, strongly emit light.

The enhancement of the light-sensitiveness of photographic printingmaterial containing diazo compounds attained according to the process ofthe present invention which enables an essential shortening of the timeof exposure is due to the fact that either the sphere of absorption ofthe diazo compounds is enlarged by the addition of the sensitizers orthat the absorption is displaced into a region which is better adaptedto the emission spectrum of the sources of light actually applied. Inconsequence thereof the effect attained according to the presentinvention varies according to the source of light applied.

As sensitizers there may, for instance, be used polynuclear aromatichydrocarbons or the derivatives thereof. These substances are preferablyused in the form of water-soluble compounds, for instance as sulfonicacids or salt of sulfonic acids. They may then be added to the aqueousor aqueous-alcoholic coating solutions containing the diazo compounds.Anthracene compounds, phenanthrene compounds, pyrene compounds, perylenecompounds and chrysene compoundds have, for instance, a sensitizingaction if they absorb light in the manner described above.

Quinoxaline and the derivatives thereof constitute a further usefulgroup of sensitizers. The sensitizing action of these substances is, ingeneral, however, inferior to that of the hydrocarbons named above.

Many aliphatic keto-compounds are likewise suitable sensitizers, forinstance the non-volatile derivatives of acetone, such asacetone-sulfonic acid or an acetone-sulfonic acid substituted bychlorine. Pyroracemic acid may also be used. Croconic acid is avery'suitable sensitizer. These 5 acids are likewise preferably used inthe form of water-soluble salts, for instance as sodium salt orpotassium salt.

Some coumarins, especially hydroxy-coumatins, may also be used assensitizers. Furthermore, pseudoazimides are useful.

The various sensitizers named are, on exposure to light, not altered toa noticeable extent. There may, however, also be such sensitizers as, byaction of light, undergo a visible alteration if the substances producedfrom the sensitizers on exposure to light have no detrimental action inthe finished prints. The yellow, very light-sensitive diazo compounds,for instance amino-diazo-compounds which are applied, as is known, fordiazotype purposes and show a relatively strong absorption within theregion .of 3300 to 4400 Angstrom, may be used as sensitizers. If diazocompounds are used as sensitizers special care must be taken that thelight-sensitive layers bleach out on exposure to light, i. e. that bythe coupling of the decomposition product of the one diazo compound withthe other diazo compound not yet decomposed a dyestufl'. is not producedduring the exposure 'to light. This may be attained by a suitableselection of the sensitizer or by the addition of 'a sufilcient portionof acid to the light-sensitive layer. Besides the diazo compounds theremay be used as sensitizers the reaction products of diazo compounds andsulfites,.

namely the diazo-sulfonates.

Colorless or only slightly colored substances are generally preferred assensitizers. Dyestuiis, i. e. compounds containing auxochromes, such ashydroxyl groups or amino groups, besides the chromophores, for instancethe azo group, the nitro group or the nitrose group, are often lesssuitable as sensitizers, this being probably due to the fact that thefiltering action which superimposes the sensitizing action is sometimesvery strong in the case of such dyestuffs so that on using an unsuitablesource of light an enhancement of the sensibility cannot be observed asa total result. These conditions have to be taken into consideration ifdyestuffs are used as sensitizers.

By means of the afore-named sensitizers the light-sensitiveness ofrelatively light-insensitive diazo compounds may be enhanced to amultiple so that they then satisfy the practical requirements. Colorlessdiazo compounds of thebenzene series which are free from amino groupsmay be sensitized with particularly good success, for example diazophenols and diazo phenol ethers. Diazo phenol alkyl ethers i. e. thediazotization products of p-am'sidine, o-anisidine and similar alkylethers of amino-phenols are particularly well suitable for the purposeof the invention. Other suitable colorless diazo compounds are mentionedin the co-pending application 276,420. Slightly colored compounds, for

instance the tetrazotized dianisidine, may, likewise be sensitized.

The proportion of the sensitizers present in the photographic printingmaterial may be just as large as that of the diazo compounds. eral,however, an effect may be produced by an essentially smaller quantity ofthe sensitizer than that named above. In many cases a few percentagescalculated on the diazo-compound are sufiicient. But within certainlimits there exists a proportionality between thev enhancement ofsensitizers added. Additions usual in diazotypeprocesses may be given tothe solutions. If colorless diazo compounds are used, it is advisable toadd bleaching-out dyestufls to the solutions; the

In genprocess of exposure to light may thus be weli observed. The usualsupports, such as paper and films of all kinds may be used. If films areapplied, the sensitizing eflect is ingeneralmanifested particularlywell.

It is also possible to use several sensitizers simultaneously. Azocomponents are suitably contained in the sensitized photographicprinting material containing diazo compounds, so that the prints may bedeveloped by the dry method.

The following examples serve to illustrate the invention, but they arenot intended to limit it thereto:

(1) A film of regenerated cellulose is impregnated with a solutioncontaining in 1000 cc. of water 15 grams of the double salt of zincchloride of the diazo compound from l-amino-S-methyl- 4-methoxybenzene,15 grams of tartaric acid, 12 grams of R-salt and 10 gramsv of potassiumanthracene-2.7-disulfonate. By an exposure to light for about 1 minuteunder an arc lamp of 12 amperes and a development with gaseous ammonia,photographic prints of good properties may be obtained with the aid ofthe dried material. By the addition of the anthracene compound theexposure time is reduced to the sixth to seventh part of the timeotherwise required. The sensitivity to light may be further enhanced byan addition larger than that named above of potassiumanthracenedisulfonate, the gradation becoming flatter. Insteadof theanthracene compounds named there may for instance be usedbeta-anthracene-monosulfonic acid and the sul- Ionic acids ofphenanthrene or the water-soluble salts thereof.

(2) A foil of acetyl cellulose is coated on one side with a solutioncontaining per 500 cc. of water and 500 cc. of alcohol 110 grams of thezinc chloride double salt of the diazo compound from2.4-dimethoxy-l-aminobenzene, 100 grams of citric acid, 60 gram ofphenol and grams of the mixture of potassium perylene-3.9-disulfonateand potassium perylene-3.l0-disulfonate the light-sensitiveness and thequantity of the (cf. Zentralblatt, 1927, vol. I,'page 1833). A foil thusprepared is very well suitable for the production of reflex copies.

(3) Photographic crude paper is coated with a solution containing in1000 cc. .of water 25 grams of the diazo compound from l-amino-4-ethoxy3-benzene-sulfonic acid, 15 grams of tartaric acid, 20 grams of G-saltand 15 grams of potassium croconate; the paper is then dried. With thehelp of a paper thus coated diazotypes may be obtained.

(4) A cellulose-hydrate film is bathed in an aqueous solution containingper 1000 cc. of water 12 grams of the zinc chloride double salt of thediazo compound from 4-amino-1-phenoxybenzene, 8 grams of R salt, 15grams of tartaric acid and 11 grams of quinoxaline; the material is thendried. Instead of the quinoxaline serving as a sensitizer there may beused the derivative of this compound, for instance the6.7-dimethylquinoxaline, the quinoxaline-2.3-dicarboxylic acid, the6.7-dimethyl-2.3-dimethoxy-quinoxaline or the5.6-benzo-2.3-dimethyl-quinoxaline or the sulfonation products thereof.

(5) 15 grams of the zinc. chloride double salt of the diazo compoundfrom 2.4-dimethoxy-1- aminobenzene, 12 grams of tartaric acid, 12 gramsof R-salt and 7.5 gramsof the sulfate of the diazo compound from4-amin'o-diphenylamine are dissolved in 1000 cc. of Water.Light-sensitive layers prepared with the help of the solution thusobtained are distinguished by an enhanced sensitivity to light incomparison with the layers obtained with the help of a similar solutionwhich is free iromthe diazo compound of 4-amino-diphenylamine.

(6) The process is carried out as it is described in example but as asensitizer 5 grams oi? esculetin or another similar coumarine derivativeare used, for instance 5.7-dlhydroxy 4-methylcoumarine ('7) A film fromregenerated cellulose is rendered sensitive to light with the help of asolution of 17 grams of the diazo compound from2.5-dimethoxy-l-aminobenzene (zinc chloride double salt), 12 grams ofresorcine, 20 grams of tartaric acid, 5 grams of boric acid and 20 gramsof sodium acetone-sulfonate in 1000 cc. of water. The sodiumacetone-sulfonate acting as a sensitizer may be replaced by the sodiumsalt of an acetone-sulfonic acid substituted by chlorine or the sodiumsalt of pyroracemic acid.

We claim:

1. Light-sensitive material which consists of a carrier having a layercomprising a diazo compound of the group consisting of diazo phenol,diazo phenol ether and diazo phenol alkyl ether all free from aminosubstituents of small lightsensitiveness and a sensitizer-consisting inan oraanic compound free from heavy metal which compound shows a strongabsorption of light within the sphere of the spectrum adjacent to thesphere of absorption of the said diazo compound towards the long wavesthe said sensitizer being a member of the group consisting ofpolynuclear aromatic hydrocarbons, aliphatic keto compounds,quinoxalines, coumarines and pseudoazimides.

2. Light-sensitive material according to claim 1 wherein the saidsensitizer is water-soluble.

3. Light-sensitive material according to claim 1 wherein the saidsensitizer is a water-soluble sulfonated compound. a

4. Light-sensitive material which consists of a carrier having a layercomprising a diazo compound of the group consisting of diazo phenol,diazo phenol ether and diazo phenol alkyl ether all free from aminosubstituents of small lightof diazo phenol, diazo phenol ether and diazophenol allq'l ether all free from amino substituents of smalllight-sensitiveness and a sensitizer consisting in an organic compoundfree from heavy metal which compound shows a strong absorption of lightwithin the sphere of the spectrum adjacent to the sphere of absorptionof said diazo compound towards the long waves the said sensitizer beinga member of the group consisting of polynuclear-aromatic hydrocarbons,aliphatic keto compounds, 'quinoxalines, coumarines and pseudoazimides.

6. Light-sensitive material according to claim 5 wherein the saidsensitizer is water-soluble.

7. Light-sensitive material according to claim 5 wherein the said,sensitizer is a water-soluble sulfonated compound.

8. Light-sensitive material which consists of a carrier having a layercomprising a substantially colorless diazo compound of the groupconsisting of diazo phenol, diazo phenol ether and diazo phenol alkylether all free from amino substituents of small light-sensitiveness anda sensitizer consisting in a water-soluble sulfonated aromatichydrocarbon with three to five condensed benzene rings.

9. Light-sensitive material which consists of a carrier having a layercomprising a substantially colorless diazo phenol ether of smalllight-sensisensitiveness and a sensitizer consisting in a iwater-soluble sulfonated aromatic hydrocarbon carrier having a layercomprising a substantially colorless diazo compound or the groupconsisting tiveness and a small percentage calculated on thediazo-compound, a sensitizer consisting in an organic compound free fromheavy metal which compound shows-a strong absorption of light within thesphere of the spectrum adjacent to the sphere of absorption of the saiddiazo phenol ether towards the long waves the said sensitizer being amember of the group consisting of polynuclear aromatic hydrocarbons,aliphatic keto compounds, quinoxalines, coumarines and pseudoazimides.

10. Light-sensitive material according to claim 9 wherein the saidsensitizer is water-soluble.

ll. Light-sensitive material according to claim 9 wherein the saidsensitizer is a water-soluble sulfonated compound.

12. Light-sensitive material which consists of a carrier having a layercomprising a substantially colorless diazo phenol ether of smalllight-sensitiveness and a sensitizer consisting in a watersolublesulfonated aromatic hydrocarbon with three to five condensed benzenerings.

13. Light-sensitive material which consists of a carrier having a layercomprising asubstantially colorless diazo phenol alkyl ether of smalllight-sensitiveness and as a sensitizer an alkali metalanthracene-2.7-disulfonate.

MAXIMILIAN PAUL SCHMIDT. GOTTLIEB vor: POSER.

